1. Field of the Invention
This invention relates to a process for producing methyl ethyl ketone and more particularly it relates to a process for producing methyl ethyl ketone by oxidizing 1-butene by means of an oxygen complex.
2. Description of the Prior Art
Methyl ethyl ketone (hereinafter referred to often as MEK) is used as the solvent for nitrocellulose, acetylcellulose, etc. and also used in the process for dewaxing lubricating oils and further used as a raw material for methyl ethyl ketone peroxide which has been produced in a large amount as a curing agent for unsaturated polyester resins and as a polymerization initiator; thus MEK is an important intermediate product in chemical industries.
Heretofore the process for producing MEK is roughly classified into (1 ) a sec-butanol dehydrogenation process and (2) a n-butane oxidation process. In the dehydrogenation process, MEK is produced according a two-stage process wherein from n-butene is prepared sec-butanol, which is then dehydrogenated at 430.degree.-450.degree. C. and 3 atm by means of a Zn-Cu catalyst, and the yield of MEK is 80%. On the other hand, the n-butane oxidation process wherein acetic acid is produced at the same time includes a non-catalyst type oxidation process and a process by means of cobalt acetate. It has been regarded that according to the former, the reaction is carried out at 15-20 atm and 180.degree. C. using a liquid primary oxidation product as solvent and the yield of MEK is 13 %, while according to the latter, the reaction is carried out at 54 atm and 175.degree. C. and the yield of MEK is 17% (see K. Werssemel & H. J. Arpe, Industrial Organic Chemistry, translated by T. Mukaiyama, PP. 165 and 266, Tokyo Kagaku Dojin (1978)). Since the processes are both carried out under conditions of relatively high temperatures and pressures and hence the amount of by-products is large, the selectivity of the reaction and the improvement in yield have raised a problem. Further, when excess dissolved oxygen is released into the gas phase part of the reactor, it mixes with butane, MEK and the like gas to have a possibility of troubles such as explosion whereby a countermeasure thereto is required (see Revised Complete Production Flow Sheet, edited by Kihara et al, Vol. II, page 286, Kagakukogyosha (1978)). Thus, it has a great meaning that MEK can be produced from 1-butene selectively even at a single step.
Further, as a process for oxidizing a terminal olefin utilizing the oxidative force of palladium chloride (Pd(2)Cl.sub.2), Wacker process has been well known. According to this process, a redox system aqueous solution of Pd(2)/Pd(0) and Cu(2)/Cu(1) is employed and propylene oxidation is relatively easy, but in the case of 1-butene and higher olefins of 5 or more carbon atoms, since these olefins are hardly soluble in water, the reaction rate is notably retarded (see J. Tsuji, Catalyst, 25, 452 (1983)); hence it has been regarded that the production of MEK according to 1-butene oxidation by means of the oxidative force of Pd(2)Cl.sub.2 has not been practically carried out (see T. Tamura, Catalyst, 21, 167 (1979)).
On the other hand, as to the oxygen complexes which function as an effective oxidizing agent for the oxidization reactions of organic substances, various studies have been made as a modeling of the respiratory reaction of living bodies (see H. Tsuchida, Introduction to Chemistry, No. 20, PP. 30-40 (1978)). Their examples are iron-heme protein in mammals and copper-heme protein in molluscs. In these proteins, the oxidative state of iron or copper is a lower valence state.
Usually, in the case of metal ions capable of taking various valences, lower valence ions turn to higher metal ions when they are contacted with oxygen as shown in the following equation: EQU Cu(1)+1/4O.sub.2 +1/2H.sub.2 O.fwdarw.Cu(2)+OH.sup.- ( 1) EQU Fe(2)+1/4O.sub.2 +1/2H.sub.2 O.fwdarw.Fe(3)+OH.sup.- ( 2)
However, in hemoglobin and hemocyanin, even when Fe(2) and Cu(1) are contacted with oxygen, the metal ions are not oxidized, but oxygen is coordinated with the metal ions in the form of oxygen molecule, that is, an oxygen complex is formed, which is stably existent.
The thus combined oxygen molecule is activated through its coordination with the metal ions to oxidize many organic substances at as low temperatures as the body temperatures of living bodies, and the reaction heat constitutes the energy source of living bodies. However, when such protein complexes are separated from living bodies, they are so unstable that the metal ions are readily oxygen-oxidized; hence the complexes cannot be a practical oxidizing agent. Thus, it has been earnestly desired in respect of application to a commercial oxidation reaction to use an artificial compound as an oxidizing agent and to find a complex capable of forming a stable oxygen complex by combining the compound with a suitable transition metal.
The object of the present invention is to provide, in view of the above prior art, a process for producing methyl ethyl ketone wherein 1-butene is subjected to oxygen-oxidation under mild conditions whereby MEK can be produced selectively and with a high yield.